Apparatus for defrosting cooling units of absorption refrigeration systems

ABSTRACT

In an hermetically sealed absorption refrigeration system employing an inert gas, refrigerant vapor expelled from solution in a generator by heating normally is conducted through a main vapor line to a condenser in which the vapor is liquefied and from which liquid refrigerant is conducted to an evaporator to produce useful refrigeration. Frost accumulating on the evaporator is melted by such expelled vapor which is diverted from the main vapor line and flows directly to the evaporator through a by-pass connection. The main vapor line and by-pass connection have places for collecting and trapping liquid resulting from condensation of the vapor and in which trapped liquid offers resistance to flow of vapor therethrough. When the liquid trapped in the main vapor line offers sufficient resistance to stop flow of vapor therethrough, vapor is diverted from the main vapor line through the by-pass connection, such diverted vapor being capable of passing through any liquid in the by-pass connection and flowing to the evaporator to melt frost formed thereon. When vapor is diverted into the by-pass connection the pressure of vapor acting on the liquid trapped in the main vapor line is reduced which causes removal of liquid therefrom, thereby reducing the resistance it offers to flow of vapor therethrough below that offered by liquid trapped in the by-pass connection. When this occurs normal flow of vapor to the condenser takes place through liquid trapped in the main vapor line.

United States Patent 1 Kiigel et al.

[ June 26, 1973 APPARATUS FOR DEFROSTING COOLING UNITS OF ABSORPTION REFRIGERATION SYSTEMS [75] Inventors: Wilhelm Georg Kiigel, Lidingo; Bernt Henry Roland Dahlqvist, Motala, both of Sweden [73] Assignee: Aktiebolaget Electrolux, Stockholm,

Sweden [22] Filed: Oct. 6, 1971 [21] Appl. No.: 187,078

[30] Foreign Application Priority Data Oct. 8, 1970 Sweden ..13626/70 [52] US. Cl 62/278, 62/490, 62/496 [51] Int. Cl. F25b 15/10 [58] Field of Search 62/81, 110,278,

[56] References Cited UNITED STATES PATENTS 2,285,884 6/1942 Ashby 62/495 2,468,104 4/1949 Phillips 62/110 X 2,881,598 4/1959 Hellstriim 62/490 X 2,956,415 10/1960 Kiigel 62/81 3,163,997 l/1965 Stierlin.... 62/81 X 3,277,665 10/1966 Batson.... 62/8] X 3,338,062 8/1967 Kiigel 62/490 X 3,580,004 5/1971 Kfigel 62/490 X Primary Examiner-William F. ODea Assistant ExaminerPeter D. Ferguson Att0rney-Edmund A. Fenander [5 7] ABSTRACT In an hermetically sealed absorption refrigeration system employing an inert gas, refrigerant vapor expelled from solution in a generator by heating normally is conducted through a main vapor line to a condenser in which the vapor is liquefied and from which liquid refrigerant is conducted to an evaporator to produce useful refrigeration. From accumulating on the evaporator is melted by such expelled vapor which is diverted from the main vapor line and flows directly to the evaporator through a bypass connection. The main vapor line and by-pass connection have places for collecting and trapping liquid resulting from condensation of the vapor and in which trapped liquid offers resistance to flow of vapor therethrough.

When the liquid trapped in the main vapor line offers sufficient resistance to stop flow of vapor therethrough, vapor is diverted from the main vapor line through the by-pass connection, such diverted vapor being capable of passing through any liquid in the by-pass connection and flowing to the evaporator to melt frost formed thereon. When vapor is diverted into the by-pass connection the pressure of vapor acting on the liquid trapped in the main vapor line is reduced which causes removal of liquid therefrom, thereby reducing the resistance it offers to flow of vapor therethrough below that offered by liquid trapped in the by-pass connection. When this occurs normal flow of vapor to the condenser takes place through liquid trapped in the main vapor line.

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APPARATUS FOR DEFROSTING COOLING UNITS OF ABSORPTION REFRIGERATION SYSTEMS BACKGROUND OF THE INVENTION 1. Field of the Invention In hermetically sealed absorption refrigeration systems employing inert gas, refrigerant vapor expelled by heating in a generator is liquefied in a condenser and condensed refrigerant flows to an evaporator to evaporate in the presence of the inert gas to produce useful refrigeration. Such expelled vapor, which is at an elevated temperature, is conducted from time to time to the evaporator in a path of flow which bypasses the condenser, whereby the expelled vapor melts the frost formed on the evaporator.

2. Description of the Prior Art It has been proposed heretofore to conduct expelled vapor at an elevated temperature to the evaporator in a line which by-passes the condenser and has a trap in which liquid collects to block flow of expelled vapor therethrough and from which liquid is removed from time to time by heating to open the bypass line and initiate defrosting. Such removal of heat is effected either by bodily removing liquid from the trap or by evaporating the liquid and actuating a heater by a time switch. Defrosting is not self-starting with this prior art proposal which is objectionable. Further, the time switch not only is costly but requires manual adjustment which often necessitates servicing in the field which also is objectionable.

It also has been proposed heretofore to employ a bypass line having a trap arranged to collect liquid resulting from condensation of expelled refrigerant vapor in accordance with the so-called cold wall principle. Defrosting is effected during the interval of time it takes for a definite quantity of liquid to collect in the trap. When this occurs defrosting stops and defrosting is again initiated after sufficient liquid continues to collect in the trap whereby all of the liquid can be removed therefrom by siphon action. This prior art proposal operates in such manner that the intervals of time between defrosting periods are long which is objectionable. Also, when defrosting does commence, the quantity of heat required to melt the frost formed on the evaporator is great. These factors make this prior art arrangement sensitive to manufacturing tolerances. In some instances more heat is supplied to the evaporator by the expelled vapor than is actually required for defrosting for the reason that the capacity of this prior art arrangement must be adequate to defrost even under adverse operating conditions. This often produces an excessive rise in temperature of the space cooled by the evaporator which is objectionable.

SUMMARY OF THE INVENTION It is an object of our invention to provide an improve ment for automatically initiating and terminating defrosting of an evaporator of an inert gas type absorption refrigeration system by relatively small quantities of heat developed within the system and frequently made available for defrosting purposes responsive solely to changes in an operating condition in the system. We accomplish this by providing places in the main vapor line and a by-pass connection for collecting and trapping liquid resulting from condensation of vapor and in which liquid offers resistance to flow of vapor therethrough.

Refrigerant vapor expelled from solution by heating normally is conducted through the main vapor line to a condenser in which the vapor is liquefied and from which liquefied refrigerant is conducted to the evaporator to produce useful refrigeration. Frost accumulating on the evaporator is melted by such expelled vapor which is diverted from the main vapor line and flows directly to the evaporator through the by-pass connection.

When the liquid trapped in the main vapor line offers sufficient resistance to stop flow of vapor therethrough, vapor is diverted from the main vapor line through the by-pass connection, such diverted vapor being capable of passing through any liquid trapped in the by-pass connection and flowing to the evaporator to melt frost formed thereon. When vapor is diverted into the bypass connection the pressure of vapor acting on the liquid trapped in the main vapor line is reduced which causes removal of liquid therefrom, thereby reducing the resistance it offers to flow of vapor therethrough below that offered by liquid trapped in the by-pass connection. When this occurs normal flow of vapor to the condenser takes place through liquid trapped in the main vapor line.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 diagrammatically illustrates an absorption refrigeration system of the inert gas type embodying our invention;

FIGS. 2, 3 and 4 are fragmentary views of parts shown in FIG. 1 to illustrate the different levels that liquid in the parts assumes during operation of the system;

FIGS. 5 to 8, inclusive, are fragmentary views of parts like those shown in FIG. 1 diagrammatically illustrating other embodiments of the invention;

FIG. 9 is a fragmentary view of parts shown in FIG. 1 illustrating the refrigeration system provided with a thermostat control;

FIGS. 10 and 11 are fragmentary views of parts shown in FIG. 1 illustrating other forms of heating devices for the refrigeration system; and

FIG. 12 is a view similar to FIG. 10 illustrating the refrigeration system provided with a thermostat control.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing we have shown our invention in connection with an hermetically sealed absorption refrigeration system of a uniform pressure type in which an auxiliary pressure equalizing gas is employed. Air-cooled systems of this type are well known and include a cooling unit or evaporator E which is arranged to abstract heat from the thermally insulated interior of a refrigerator cabinet 40. Refrigerant fluid, such as ammonia, passes through a conduit 23 into the evaporator E and evaporates and diffuses therein into an inert gas, such as hydrogen, to produce a refrigerating effect. The resulting gas mixture of refrigerant and inert gas flows from evaporator E through a conduit 27, an outer passage of gas heat exchanger 25 and vertically extending conduit 28 into an air-cooled absorber comprising an absorber vessel 10 and an absorber coil 17.

In the absorber refrigerant vapor is absorbed by a suitable absorbent, such as water, for example, which i is introduced into coil 17 through a conduit 16. The hydrogen or inert gas, which is practically insoluble and weak in refrigerant, is returned to evaporator E through an inner passage of gas heat exchanger 25 and a conduit 41.

Since the column of gas rich in refrigerant vapor and flowing from the evaporator E to the absorber coil 17 is heavier than the column of gas weak in refrigerant and flowing from the coil to evaporator E, a force is produced within the system for causing circulation of inert gas in the manner described. This is due to the difference in specific weight of the aforementioned columns of gas rich and weak, respectively, in refrigerant vapor.

Enriched absorption liquid, which also is referred to as absorption solution, is conducted from the vessel through an outer passage of an elongated liquid heat exchanger 11 into a conduit 13 connected to the lower end of a vapor-liquid lift pump 12 of a generator or vapor expulsion unit 42. The generator comprises a heating tube 14 having the vapor-liquid lift pump 12 in thermal exchange relation therewith at 9, as by welding, for example. By heating the generator, as by an electrical heating element 14 connected by conductors 48 to a source of electrical supply, liquid from the liquid heat exchanger 11 is raised by vapor-liquid lift action through pump 12 into the upper part of standpipe 15. The liberated lifting vapor entering standpipe 15 flows through a vapor space 31 of the stand-pipe and a vapor conduit 19 which extends downward and is connected at 43 to an elevated horizontal part 18 of the liquid heat exchanger 11 which is at the level I.

The vapor from conduit 19 passes in a horizontally extending direction in intimate physical contact with absorption solution enriched in refrigerant which is flowing through the outer passage of the liquid heat exchanger ll. The part 18 of the liquid heat exchanger 11 serves as an analyzer in which water vapor accompanying refrigerant vapor is removed from the latter by condensation. There is a small liquid head in the analyzer or horizontal part 18 which provides a liquid seal between the lower ends of conduits l9 and 20 and through which vapor passes by bubbling therethrough. The vapor passes upward from the analyzer or horizontal part 18 of the liquid heat exchanger 11 at 43 into the conduit 20 which may be referred to as a part of the vapor line being described and is connected to a rectifier 21 in which condensation of absorption liquid vapor accompanying refrigerant vapor also is effected. Refrigerant vapor flows from rectifier 21 into an aircooled condenser 22 having heat dissipating surfaces or heat transfer fins 44. Refrigerant vapor is liquefied in the condenser 22 and liquefied refrigerant is returned to evaporator E through the conduit 23 to complete the refrigerating cycle.

Liquid refrigerant flows by gravity in the evaporator E, the refrigerant flowing in parallel flow with the inert gas in a low temperature section 24 and in a higher temperature section 26 of the evaporator E. The weakened absorption solution, from which refrigerant has been expelled, is conducted from standpipe l5, inner passage ofliquid heat exchanger 11 and conduit 16 into the upper part of the absorber coil 17. Circulation of absorption solution in the manner just described is effected by raising of liquid to a high level in stand-pipe 15 from which liquid can flow by gravity to the upper end of absorber coil 17 through conduit 16. The outlet end of the condenser 22 is connected by a conduit 30 to a part of the gas circuit, as at the upper end of the conduit 28, for example, so that any inert gas which may pass through the condenser 22 can flow into the gas circuit. Any unevaporated refrigerant at the outlet end of the higher temperature evaporator section 26 flows therefrom to the outer passage of the gas heat exchanger 25 through a conduit 29 formed as a liquid trap.

The refrigerating effect produced by the upper evaporator section 24, which is adapted to be operated at temperatures substantially below freezing, is primarily utilized to effect cooling of an upper frozen food space 40a which is defined by a partition 49 and the thermally insulated walls of the cabinet 40. The refrigerating effect produced by the lower evaporator section 26, which is adapted to be operated at a higher temperature than that of evaporator section 24 and also desirably below freezing, is primarily utilized to cool air in an unfrozen food space 40b. A plurality of heat transfer fins 50 may be provided on the evaporator section 26 to promote cooling of air in the unfrozen food space 4%.

Frost accumulates on both the evaporator sections 24 and 26, such accumulation of frost taking place much more slowly in the upper space 40a than in the lower space because the need for gaining access into the former is considerably less than for the latter. If a layer of frost of considerable thickness were allowed to accumulate and form on the lower evaporator section 26, the efficiency of the refrigeration system would be reduced considerably and the system would operate for longer periods of time to maintain the unfrozen food space 40b at a desired low temperature than would otherwise be the case.

In order to defrost the evaporator section 26, refrigerant vapor expelled in vapor expulsion unit 42 and at an elevated temperature is conducted therefrom to the evaporator E in a path of flow which includes the pump 12, vapor space 31 of standpipe 15, upper part of vapor conduit 19 and a by-pass connection 51 which bypasses the condenser 22 and includes conduit sections 32, 33, 34 and 35. By introducing hot expelled refrigerant vapor into the evaporator E the partial pressure of the refrigerant vapor in the evaporator increases and the temperature thereof will rise above the freezing temperature of water. In this manner the frost formed on the evaporator E is melted very rapidly by the hot vapor supplied thereto from generator 42 in a path of flow which by-passes the condenser 22.

The by-pass connection 51 is connected to a region 52 of the evaporator E at which inert gas partially enriched in refrigerant vapor and flowing from the upper evaporator section 24 is about to enter the lower evaporator section 26. The hot vapor introduced into the evaporator E at the region 52 mixes with inert gas which has been discharged from the upper evaporator section 24 and flows in parallel flow therewith into the lower evaporator section 26. With this arrangement it is possible to continue to store food at a safe refrigerating temperature in the frozen food space 40a. Also, defrosting of the lower evaporator section 26 can be effected sufficiently rapidly so that the temperature of the unfrozen food space 40b only increases a relatively small amount. In this way food can be stored in the space 40b at a safe refrigerating temperature during the interval of time the higher temperature evaporator section 26 is being defrosted.

In accordance with our invention the by-pass connection includes the conduit sections 32, 33, 34 and 35 which provide a path of flow for hot vapor from the vapor space 31 of the standpipe to the region 52 of the higher temperature evaporator section 26. The conduit section 32 is connected to the vapor space 31 at a comparatively high point 36 so that the by-pass connection 51 leading to the evaporator E, which is generally positioned higher than the vapor-expulsion unit 42, will be short.

The conduit sections 32, 33 and 34 form a U-shaped trap 53 with the conduit section 32 forming the right arm of the trap which extends downward from the point 36. The conduit section 32 defines a passageway having an inner diameter which permits vapor to pass through liquid therein. The conduit section 34, which forms the left arm of the trap 53, extends upward to a point 54 which is higher than the point 36 by a distance which is greater than the difference in the vertical height of the liquid levels of the liquid columns in conduits 19 and of the analyzer 18. From the point 54 at the upper end of the conduit section 34 the conduit section 35 of the by-pass connection 51 slopes downward to the region 52 of the evaporator E at which it is connected thereto. It will be seen that the vapor conduit 20 extending upward from the analyzer 18 at 43' is throttled at 37 at a region below the rectifier 21 for a purpose that will be explained presently.

When the heating element 14 of the refrigeration system of FIG. 1 has been disconnected from the source of electrical supply and the vapor expulsion unit or generator 42 is at ambient air temperature, the solution in the different parts of the absorption solution circuit is at approximately the same level I. The trap 53 can be empty or may hold a small quantity of liquid which is at the same level II in both arms thereof.

When operation of the refrigeration system is started by connecting the conductors 48 to a source of electrical supply and heat is supplied to the heating member 14 by the heating element 14, solution is raised in the pump pipe 12 by vapor-liquid lift action. This raised solution increases the height of the liquid column in standpipe 15 from the level I to the level III, as shown in FIG. 2, at which time liquid weak in refrigerant will flow by gravity from standpipe 15 to the upper end of absorber coil 17 in a path of flow which includes the inner passageway of liquid heat exchanger 11 and conduit 16.

While this is taking place vapor liberated from the raised absorption solution passes into the vapor space 31 where its pressure increases. Vapor at an increasingly higher pressure in the space 31 acts on liquid in the right arm 32 of the trap 53, and, when the liquid in this arm is depressed to the level IV, as shown in FIG. 2, vapor at an elevated temperature can pass through liquid in the trap in the direction of the arrow 38 and flow to the evaporator E through the conduit sections 34 and 35.

Since the conduit section 32, other than at the region 36 at which it is connected to the conduit 19, is spaced therefrom by a gap 55, the wall of the conduit section 32, and also the walls of the conduit sections 33 and 34, always are at a somewhat lower temperature than that of the vapor conduit 19 during operation of the refrigeration system. When these conduit sections are free of liquid expelled vapor passing therein from vapor space 31 will condense, such condensation taking place in accordance with what may be referred to as the cold wall" principle.

In the event the trap 53 does not contain liquid when operation of the refrigeration system is started, vapor liberated into the space 31 will immediately flow to the evaporator E through the trap 53 and conduit section 35. Any condensate formed at the inner surface of the conduit section 34 collects in the U-shaped trap 53. Vapor in the vapor space 31 continues to act on the liquid in the right arm 32 of the trap 53 and forces the column of liquid in the left arm 34 to the level V, as shown in FIG. 2. Due to condensation of vapor in the trap 53 the difference between the liquid levels V and IV increases.

While the foregoing is taking place the vapor in the vapor space 31 at the same time is acting on the column of liquid in the conduit 19 and forcing it downward from the level I to the level VI, as shown in FIG. 2. When this occurs vapor in the space 31 can pass through the liquid head or seal in the analyzer 18 from the conduit 19 to the conduit 20. This causes the column of liquid to rise slightly in the conduit 20 which is dependent upon the temperature prevailing in this conduit and rate at which refrigerant vapor is expelled out of solution in the vapor expulsion unit or generator 42.

The manner in which operation of the refrigeration starts, as just explained, takes place very rapidly and relatively small quantities of vapor initially flow directly from the vapor space 31 to the evaporator E through the by-pass connection 51. This is due to the fact that/the liquid seal formed in the trap 53 builds up very fast so that the difference in height of the liquid columns in its arms 32 and 34, that is, the liquid head, is larger than the liquid head in the analyzer 18 which functions to resist flow of vapor therethrough from the conduit 19 to the conduit 20.

When the column of liquid in the arm 34 of the trap 53 reaches the level VII, as shown in FIG. 3, the liquid head in the trap offers greater resistance to flow of vapor therethrough than the liquid head in the analyzer 18 and vapor in the space 31 will now pass through liquid in the analyzer and flow upward in the conduit 20, as indicated by the arrow 39 in FIG. 3. When this occurs normal operation of the refrigeration system takes place and the evaporator E functions to produce useful refrigeration in the manner explained above.

The throttling portion 37 in the conduit 20 of the main vapor line leading to the condenser 22 desirably is circular and of such size that water vapor accompanying refrigerant vapor and removed therefrom by condensation in the rectifier 21 flows downward in the upper part of the conduit 20 and, since it cannot pass the throttling portion 37, is retained above the latter. The liquid above the throttling portion 37, which may be about 2 mm. in diameter, is acted upon by the pressure of the vapor in the conduit 20 below the throttling portion which increases slightly. The height of the liquid column formed in conduit 20 above the throttling portion 37 increases from the level VIII to the level IX, as indicated in FIG. 3.

After an interval of time of normal operation of the refrigeration system, which desirably is from 1 to 2 hours, the combined height of the liquid head or column above the throttling portion 37, which is the difference between the levels VIII and IX, and the liquid head in the analyzer 18, which is the difference between the levels I and VI, is greater than the height of the liquid head or column in the trap 53 which is the difference between the levels VII and X. In this connection it should be understood that the liquid columns just referred to and in the throttling portion 37, analyzer 18 and trap 53 define liquid seals which offer resistance to flow of vapor therethrough.

When the operating condition just described is reached the vapor from vapor space 31 will flow through the trap 53 and vapor by-pass connection 51 directly to the evaporator E and the flow of vapor in the main vapor line from space 31 through the analyzer 18 stops, as indicated in FIG. 4. This flow of vapor through the trap 53 is indicated by the arrow 57 and will last for an interval of time of about 30 to 90 seconds. When vapor flows through the trap 53 the pressure prevailing in the vapor space 31 will decrease so as to correspond to the pressure in the evaporator E, which forms a part of the inert gas circuit, plus the remaining liquid column in the trap 53.

When flow of vapor through the analyzer 18 stops, the vapor in the conduit 20 will not be capable of maintaining the liquid column in this conduit above the throttling portion 37. Under these conditions all or at least a greater part of the liquid in this column will flow downward past the throttling portion 37 toward the analyzer 18, as indicated by the arrow 58 in FIG. 4.

After the pressure in the vapor space 31 has de creased there may or may not be any overflow of liquid from the right arm 32 of the trap 53 into the conduit 19. If the region 36 at which the right arm 32 is connected to the conduit 19 is located relatively high above the level IV, there will be no overflow of liquid from the trap 53 into the conduit 19 or possibly only a small quantity of liquid will overflow therein. But the right arm 32 can be made comparatively short to insure that liquid will overflow from the trap. This is desirable, as pointed out above in describing what is taking place in FIG. 2, to insure flow of vapor in the vapor by-pass connection 51 through the liquid head or seal in trap 53 for a slightly longer interval of time before the liquid head builds up and offers sufficient resistance to flow of vapor, so that the vapor will flow from conduit 19 through the analyzer 18 in the manner explained above in describing what is taking place in FIG. 3. Accordingly, it depends upon the manner in which different parts of the refrigeration system are related to one another whether the system, after defrosting has been effected, will operate approximately as described above in connection with FIG. 2 with an increasingly longer liquid head or column in the liquid trap 53 with no significant quantity of liquid in the conduit above the throttling portion 37; or, will operate normally as described above in connection with FIG. 3 with the liquid column above the throttling portion 37 becoming increasingly longer. When the different parts of the system are related to one another in such manner that liquid is removed from the trap 53 when the vapor space 31 and evaporator E are at the same pressure, defrosting will continue for a somewhat longer interval of time but, when defrosting terminates, normal operation of the refrigeration system resumes in the manner explained above and shown in FIG. 3.

In FIG. 5 we have shown another embodiment of our invention having a vapor expulsion unit or generator 142 which differs from the generator 42 shown in the drawing and described above. It will be understood that the other parts of the refrigeration system of which the generator 142 forms a part can be like those shown in FIG. 1 and previously described.

In FIG. 5 a heating member 114 is heated by an electrical heating element 114' connected by conductors 148 to a source of electrical supply. The heating member 114 is heat conductively connected, as by welding, to a vapor-liquid lift tube 112. Absorption liquid enriched in refrigerant flows to the lower end of lift tube 112 from the absorber in a path of flow which includes the inner passage of a liquid heat exchanger 111 and a conduit 59 which is connected at 60 to a standpipe 61 below the liquid level XI therein. Liquid flows from the lower end of standpipe 61 through a conduit 62 to the lower end of the lift pump 112.

Liquid raised by the lift tube 112 is introduced into the upper end of a standpipe 115 from which it flows through the outer passage of the liquid heat exchanger 111 to the absorber. Vapor liberated from the raised liquid passes into the vapor space 131 and flows therefrom through a vapor conduit 119 which is connected at 143 to the standpipe 61 below the liquid level therein. Hence, vapor introduced into standpipe 61 bubbles through liquid in analyzer 118 and flows through the standpipe, which forms a part of the main vapor line, to the condenser.

In FIG. 5 vapor is diverted from the main vapor line by a liquid trap 153 formed by conduit sections 132, 133, 134 and 135. These conduit sections, as in the first-described embodiment, form parts of a by-pass connection 151 to the evaporator. A throttling portion 137 like the throttling portion 37 in FIG. 1 is provided in the main vapor line ahead of the analyzer 118. In FIG. 1 vapor reaches the throttling portion 37 after passing through the analyzer 18. The throttling portion 137 in FIG. 5 functions in the same manner as the throttling portion 37 in FIG. 1 and described above and further description thereof is not believed necessary.

In FIGS. 6 and 7 we have shown other embodiments of our invention in which throttling portions like the throttling portions 37 and 137 in FIGS. 1 and 5, respectively, also serve as an analyzer. In FIGS. 6 and 7 the generally similar expulsion units or generators 242 differ from the previously described generators. It will be understood that the other parts of the system of which the generators 242 form a part can be like those shown in FIG. 1 and previously described.

In FIGS. 6 and 7 the vapor-expulsion unit 242 is connected by a liquid heat exchanger 211 to the absorber in the same manner that the liquid heat exchanger 11 in FIG. 1 is connected to the absorber vessel 10 and coil 17. Absorption solution weak in refrigerant flows to the absorber through the outer passage of the liquid heat exchanger and conduit 216 to the upper end of the absorber coil and absorption solution rich in refrigerant flows from the absorber through a conduit 71, the inner passage of the liquid heat exchanger 211 and a vaporliquid lift pump 212 about which is disposed a jacket 63 forming an annular space 64 between these parts. In effect, the annular space 64 forms an extension of the outer passage of the liquid heat exchanger passage and raised liquid flows therefrom to the absorber through the outer passage of the liquid heat exchanger 211 and conduit 216.

The jacket 63 serves as a heat receiving part of the refrigeration system which is heat conductively connected, as by welding, to a heating tube 214 and a heating flue 65. The heating tube 214 is heated by an electrical heating element 214' therein which is connected by conductors 248 to a source of electrical supply. The

heating flue 65 is arranged to be heated by a gaseous fuel burner 66 connected by a conduit 67 to a source of supply of gaseous fuel. It will be evident that the heat receiving part or jacket 63 can be heated either by the heating tube 214 or the heating flue 65.-

Conduit 68 receives vapor expelled from solution in the annular space 64 in which an insert 70 is disposed to promote expulsion of such vapor from downwardly flowing solution. Vapor from space 64 and lifting vapor liberated from the raised absorption solution flows to the condenser in a main vapor line which includes the conduit 68 and a rectifier 221 having an insert 69 therein to promote condensation of water vapor accompanying refrigerant vapor, such condensate flowing downward in conduit 68 in a manner that will be described presently.

In FIG. 6 vapor is diverted from the main vapor line by a liquid trap 253 formed by conduit sections 232, 233, 234 and 235. These conduit sections, as in the previously described embodiments, form parts of a by-pass connection 251 to the evaporator. In FIG. 7 vapor is diverted from the main vapor line to the evaporator through a by-pass connection 351 which includes conduit sections 334 and 335 and has a throttling portion 237a defining a trap 353 that functions in the same manner as the trap 253 in FIG. 6.

A throttling portion 237 similar to the throttling portions 37 and 137 in FIGS. 1 and 5, respectively, is provided in the conduit 68 in FIGS. 6 and 7. As in the previously described embodiments, condensate formed in the rectifier 221 and flowing downward therefrom collects in the part of conduit 68 above the throttling portion 237. The liquid column formed above the throttling portion 237 provides a liquid seal in the main vapor line which also serves as an analyzer through which vapor from the vapor-expulsion unit 242 passes. In FIG. 7 liquid collects above the throttling portion 237a as the result of condensation at the inner wall of conduit section 335.

The embodiments of FIGS. 6 and 7 operate generally in the same manner as the previously described em bodiments. When a defrosting period commences, refrigerant vapor condenses relatively fast in the conduit sections 235 and 335 to form liquid seals in the trap 253 and the throttling portion 237a defining the trap 353. When these liquid seals are formed flow of vapor through the by-pass connections 251 and 351 stops. However, liquid is being collected in the conduit 68 above the throttling portion 237 and a liquid column is being formed above the latter which is constantly increasing in height.

A comparatively large quantity of liquid can be collected above the throttling portion 237. By locating the throttling portion 237 at different positions relative (l to the vapor expulsion unit 242 and (2) to the rectifier 221, the rate at which liquid is collected above the throttling portion 237 per unit interval of time can be varied. Also, the rate at which liquid is collected above the throttling portion 237 is influenced both by the temperature prevailing in the conduit 68 above the throttling portion during operation of the refrigeration system and by the distance from the throttling portion to the condenser. Accordingly, the throttling portion 237 desirably should be located comparatively high in the conduit 68 and relatively near the rectifier 221.

In the embodiments which have been described and illustrated in the drawing it is possible that the manner in which liquid collects above the throttling portion and forms a seal above such portion results in shorter intervals of time between defrosting periods than considered necessary or desirable. This operating condition can be corrected by an arrangement like that illustrated in the embodiment of FIG. 8 which shows a vapor expulsion unit or generator 342 similar to the generator 42 in FIG. 1 with like parts designated by the same reference numerals.

In FIG. 8 a raised wall or bar 72 is provided in the rectifier 321 which functions as a dam. Liquid condensed in the rectifier to the left of the darn 72 is diverted into the upper end of a drain conduit 73 which is connected to the conduit 20 at a region 74 below the throttling portion 37. A U-shaped trap 75 is provided at the lower end of the drain conduit 73 in which liquid collects and forms a seal in its path of flow from the rectifier 321 to the conduit 20.

The liquid seal in the trap 75 prevents vapor from bypassing the throttling portion 37 and passing directly to the rectifier 321 through the conduit 73 from the conduit 20. Liquid collecting above the throttling portion 37 results only from condensation of vapor taking place in conduit 20 between the throttling portion 37 and the dam 72. Liquid collecting in the rectifier 321 to the left of the darn 72 as the result of condensation of vapor, on the other hand, will not flow toward the region above the throttling portion 37 but instead will be diverted into the drain conduit 73 and pass into the conduit 20 and flow toward the analyzer 18. In this way the intervals of time between defrosting periods can be made longer.

In FIG. 1 the generator or vapor expulsion unit 42 in its entirety, together with a major portion of the liquid heat exchanger 11, are embodied in a body of insulation material, diagrammatically illustrated at 56, which may be retained in a metal shell or casing (not shown) having an opening at the bottom thereof. The heating tube 14 desirably is embedded in a part of the insulating material 56 which is spaced from the top and bottom ends thereof. The electrical heating element 14 is arranged to be positioned within the heating tube 14 through the bottom opening in the shell. The body of insulating material 56 reduces radiation heat losses and conserves heat with a temperature gradient in an outward direction from its center portion.

By locating the conduit sections 32, 33 and 34 of the vapor by-pass line 51 in a cooler or warmer place in the body of insulating material 56, the rate at which condensation of vapor takes place in the by-pass line 51 and liquid collects in the trap 53 can be accelerated or delayed.

It will be understood that, although not diagrammatically indicated, the vapor-expulsion units or generators 142 and 242 in the embodiments of FIGS. 5, 6 and 7 also are embodied in bodies of insulation in the same manner as the embodiment of FIG. 1. Accordingly, the traps 153, 253 and 353 in FIGS. 5, 6 and 7, respectively, can be located in the insulation in cooler or warmer places thereof to accelerate or delay the rate at which liquid collects in the trays.

It is of particular interest that our improved defrosting arrangement functions to effect defrosting automatically when heat is being supplied continuously to the vapor-expulsion unit or generator of the refrigeration system. In FIG. 1, for example, automatic defrosting takes place depending upon the relative heights of the liquid heads formed in the analyzer 18 and above the throttling portion 37 on the one hand and in the liquid trap 53 on the other hand.

Let us assume that the refrigeration system of FIG. 1 is provided with a thermostat T for controlling the supply of electrical energy to the electrical heating element 14', as shown in FIG. 9. The thermostat T includes a thermal bulb 45 which is affected by a temperature condition of the higher temperature evaporator section 26. The thermal bulb 45, which is arranged to be influenced by the temperature of air which is cooled by the higher temperature evaporator section 26, is connected by a conduit 46 to a control device 47 operatively associated with a switch 82 connected in one of the conductors 48 for supplying electrical energy to electrical heating element 14. The thermostat T is of an expansible fluid type which is charged with a suitable volatile fluid and responds to changes in a temperature condition affected by the higher temperature evaporator section 26 to operate control device 47 and the switch 37 operatively associated therewith to close and open the switch with increase and decrease, respectively, of the temperature of the air cooled by the higher temperature evaporator section 26.

When the refrigeration system is heated intermittently by the action of thermostat T, as shown in FIG. 9, instead of continuously in the manner shown in FIG. 1, defrosting of the system is effected in the manner disclosed and claimed in copending W. G. Kogel application Ser. No. 187,079, filed Oct. 6, 1971. In the aforementioned Kogel application the defrosting arrangement is such that it is self-starting each time an on or active period of the refrigeration system commences following an inactive or off" period and automatically terminates of its own accord after an interval of time. This defrosting arrangement utilizes the feature that, when the supply of heat to the vapor expulsion unit or generator 42 either is cut off or reduced sufficiently for the pressure in the vapor space 31 in FIG. 1 to fall below the pressure of the vapor and inert gas in the evaporator E, liquid in the trap 53 is removed therefrom due to this pressure differential whereby the bypass connection will be opened to allow expelled vapor to flow directly to the evaporator E to melt frost formed thereon.

In order to effect defrosting in the manner disclosed in the aforementioned Kogel application the inner diameter of the right arm 32 of the U-shaped trap 53 must be sufficiently small and substantially have the size of a pump pipe in general so that vapor cannot freely pass liquid therein; or the vertical distance between the bottom connection 33 of the U-shaped trap 53 and the region 36 at which the upper end of its right arm 32 is connected to vapor conduit 19 is sufficiently short so that the higher pressure prevailing in the inert gas circuit, of which the evaporator E forms a part, will be capable of removing the greatest part of the liquid from the trap 53 into the vapor conduit 19 in both instances just described. When the thermostat T again operates to supply heat to the vapor-expulsion unit or generator 42, defrosting is effected because the trap 53 is depleted of liquid, and, after sufficient liquid collects in the trap as the result of condensation of vapor therein, normal operation of the system will be effected in the manner explained above.

When a conventional thermostat is adjusted or set to MAXIMUM for the refrigeration system to produce maximum cooling it becomes inoperable to disconnect the heating element 14' from the source of electrical supply. Under these conditions the refrigeration system will operate continuously and defrosting will be effected automatically in accordance with our invention and in the same manner that defrosting is effected by supplying heat continuously when no thermostat is employed, as described above in connection with FIG. 1.

In FIG. 10 we have shown a vapor-expulsion unit 442 like the unit 42 of FIG. 1 heated continuously by a gas burner 76 connected by a conduit 77 to a source of supply of gaseous fuel. In FIG. 10 the gas burner 76 coacts with a heating flue 165 which is heat conductively connected to the vapor-liquid lift pump 12. When heat is supplied continuously to the refrigeration system by the gas burner 76 defrosting will be effected intermittently in the same manner as in the first described embodiment of FIG. 1 which is heated by the electrical heating element 14.

FIG. 12 illustrates the heating arrangement of FIG. 10 in which a thermostat T like the thermostat T in FIG. 9 is provided to control a valve 78 in the gas supply conduit 77. The parts of thermostat T are referred to by the same reference numerals as those designating corresponding parts in FIG. 9. The valve 78 is movable between closed and open positions, the closed position being such that a small quantity of gaseous fuel flows therethrough to prevent the burner flame from being extinguished.

It will be understood that when the refrigeration system of FIG. 1 is changed or altered in the manner explained above in connection with FIG. 9, defrosting will be effected in the manner disclosed and claimed in the aforementioned copending Kogel application. However, if the refrigeration system of FIG. 1 is operated continuously by a gas burner even when a thermostatic control is employed, as at its MAXIMUM" setting referred to above, for example, defrosting will be effected intermittently in accordance with our invention in the manner explained above in connection with FIGS. 1 to 5.

Our invention is of special importance when the refrigeration system of FIG. 1 is heated by a kerosene burner 79, as shown in FIG. 11. In FIG. 11 the lower end of a heating flue 265 is embedded in the body of insulation 56 in which a vapor-expulsion unit 542 like the vapor-expulsion unit 42 of FIG. 1 is embedded. The lower open end of the flue 265 receives the upper end of the burner 79. Liquid fuel, such as kerosene, is supplied from a storage tank (not shown) through a conduit 80 and a liquid level control 81 to the burner 79. The burner 79 can be of a type having a well to which kerosene is supplied from the liquid level control with the aid of a wick, or the burner can be of the conventional type having an adjustable wick.

Kerosene burners usually supply heat continuously to heat-operated absorption refrigeration systems and are shut off only when the need for refrigeration ceases. Hence, our improved defrosting arrangement is especially useful in a kerosene-operated refrigeration system like that shown in FIG. 11 which incorporates the system illustrated in FIG. 1 because our improvement provides automatic defrosting intermittently when heat is supplied continuously to the system.

We claim:

1. An absorption refrigeration system of the inert gas type comprising a. a gas circuit including an evaporator in which refrigerant evaporates in the presence of inert gas to produce refrigeration, said evaporator being subject to formation of frost,

b. a condenser,

c. a vapor-expulsion unit in which vapor is expelled from solution by heating,

d. means comprising a vapor line for conducting expelled vapor from the vapor space of said vaporexpulsion unit to said condenser and a condensate line for conducting condensate from said condenser to said evaporator,

e. said vapor line having at least one part constructed and arranged to provide a liquid seal formed by vaporous fluid condensed therein,

f. means comprising a by-pass connection around said condenser for conducting expelled vapor from the vapor space of said vapor-expulsion unit to said evaporator to melt frost thereon,

g. said by-pass connection having a part constructed and arranged to provide a liquid seal formed by vaporous fluid condensed therein,

h. the height of the effective liquid head of the liquid seal formed in said vapor line by condensation of vaporous fluid becoming increasingly greater responsive to flow of expelled vapor therethrough,

i. the vapor in the vapor space of said vaporexpulsion unit being conducted to said evaporator through said by-pass connection after forcing its way through the liquid seal therein responsive to increase in pressure of the vapor in the vapor space of said vapor-expulsion unit developed when the effective liquid head of the liquid seal in said vapor line exceeds the effective liquid head of the liquid seal in said by-pass connection, and

j. said part of said vapor line at which said liquid seal is formed being depleted of liquid to reduce the resistance to flow of vapor in said vapor line below the resistance to flow of vapor in said by-pass connection when the pressures in said evaporator and the vapor space of said vapor-expulsion unit are equalized.

2. An absorption refrigeration system as set forth in claim 1 in which said part of said by-pass connection providing said liquid seal therein is vertically disposed and includes a throttled zone above which vaporous fluid condenses and collects to form said liquid seal as long as the pressure of the vaporous fluid below the throttled zone is sufficiently high.

3. An absorption refrigeration system as set forth in claim 1 in/which said part of said by-pass connection providing said liquid seal therein is U-shaped and includes a downwardly extending portion communicating with the vapor space of said vapor-expulsion unit and an upwardly extending portion communicating with said evaporator.

4. An absorption refrigeration system as set forth in claim 1 in which said part of said vapor line providing said liquid seal therein is vertically disposed and includes a throttled zone above which vaporous fluid condenses and collects to form said liquid seal responsive to the presence of vaporous fluid at a sufficient pressure in said vapor line below said throttled zone.

5. An absorption refrigeration system as set forth in claim 2 in which said throttled zone is of circular form.

6. An absorption refrigeration system as set forth in claim 4 in which said throttled zone is of circular form.

7. An absorption refrigeration system of the inert gas type comprising a. a circuit for circulation of inert gas including an absorber and an evaporator subject to formation of frost, said absorber including a looped coil and a vessel into which absorption solution flows by gravity from said coil,

b. a circuit for circulation of absorption solution including said absorber and a vapor-expulsion unit, said last-mentioned circuit having conduit means for conducting solution enriched in refrigerant from said absorber to said vapor-expulsion unit, said conduit means including a part which serves as an analyzer and has a first liquid seal formed by a column of solution therein,

c. a source of heat external to the system for heating said vapor-expulsion unit to expel vapor from solution therein,

d. a condenser,

e. means comprising a vapor line including said analyzer for conducting expelled vapor from the vapor space of said vapor-expulsion unit to said condenser and a condensate line for conducting condensate from said condenser to said evaporator for evaporation therein in the presence of inert gas to produce refrigeration,

f. the expelled vapor being forced through the liquid column of said first liquid seal when expelled vapor is being conducted through said vapor line and said evaporator is producing refrigeration,

g. means comprising a by-pass connection around said condenser for conducting expelled vapor at an elevated temperature from the vapor space of said vapor-expulsion unit to said evaporator to melt frost thereon, said by-pass connection having a downwardly extending portion communicating with the vapor space of said vapor-expulsion unit and an upwardly extending portion communicating with said evaporator, said downwardly and upwardly extending portions defining a trap in which a second liquid seal is formed by vaporous fluid condensed therein,

h. the difference in height between the region at which the downwardly extending portion of said by-pass connection communicates with the vapor space of said vapor-expulsion unit and the bottom of the trap formed by said downwardly and upwardly extending portions in said by-pass connection being greater than the difference in height between the liquid surface level in said absorber vessel and the liquid level in said analyzer at the region thereof at which expelled vapor from said vapor space is introduced,

i. the upper end of said upwardly extending portion of said by-pass connection being at a level higher than that of the upper end of said downwardly extending portion of said by-pass connection by a vertical height which is greater than the difference in height between the liquid surface level in said absorber vessel and the liquid level in said analyzer at the region thereof at which expelled vapor from said vapor space is introduced, and

j. said vapor line having at least one part constructed and arranged to provide a third liquid seal formed by vaporous fluid condensed therein.

8. An absorption refrigeration system as set forth in claim 7 in which said part of said vapor line providing and collects to form said third liquidseal responsive to the presence of vaporous fluid at a sufficient pressure in said vapor line below said throttled zone.

10. An absorption refrigeration system as set forth in claim 9 in which said throttled zone is of circular form. 

1. An absorption refrigeration system of the inert gas type comprising a. a gas circuit including an evaporator in which refrigerant evaporates in the presence of inert gas to produce refrigeration, said evaporator being subject to formation of frost, b. a condenser, c. a vapor-expulsion unit in which vapor is expelled from solution by heating, d. means comprising a vapor line for conducting expelled vapor from the vapor space of said vapor-expulsion unit to said condenser and a condensate line for conducting condensate from said condenser to said evaporator, e. said vapor line having at least one part constructed and arranged to provide a liquid seal formed by vaporous fluid condensed therein, f. means comprising a by-pass connection around said condenser for conducting expelled vapor from the vapor space of said vapor-expulsion unit to said evaporator to melt frost thereon, g. said by-pass connection having a part constructed and arranged to provide a liquid seal formed by vaporous fluid condensed therein, h. the height of the effective liquid head of the liquid seal formed in said vapor line by condensation of vaporous fluid becoming increasingly greater responsive to flow of expelled vapor therethrough, i. the vapor in the vapor space of said vapor-expulsion unit being conducted to said evaporator through said by-pass connection after forcing its way through the liquid seal therein responsive to increase in pressure of the vapor in the vapor space of said vapor-expulsion unit developed when the effective liquid head of the liquid seal in said vapor line exceeds the effective liquid head of the liquid seal in said by-pass connection, and j. said part of said vapor line at which said liquid seal is formed being depleted of liquid to reduce the resistance to flow of vapor in said vapor line below the resistance to flow of vapor in said by-pass connection when the pressures in said evaporator and the vapor space of said vapor-expulsion unit are equalized.
 2. An absorption refrigeration system as set forth in claim 1 in which said part of said by-pass connection providing said liquid seal therein is vertically disposed and includes a throttled zone above which vaporous fluid condenses and collects to form said liquid seal as long as the pressure of the vaporous fluid below the throttled zone is sufficiently high.
 3. An absorption refrigeration system as set forth in claim 1 in/which said part of said by-pass connection providing said liquid seal therein is U-shaped and includes a downwardly extending portion communicating with the vapor space of said vapor-expulsion unit and an upwardly extending portion communicating with said evaporator.
 4. An absorption refrigeration system as set forth in claim 1 in which said part of said vapor line providing said liquid seal therein is vertically disposed and includes a throttled zone above which vaporous fluid condenses and collects to form said liquid seal responsive to the presence of vaporous fluid at a sufficient pressure in said vapor line below said throttled zone.
 5. An absorption refrigeration system as set forth in claim 2 in which said throttled zone is of circular form.
 6. An absorption refrigeration system as set forth in claim 4 in which said throttled zone is of circular form.
 7. An absorption refrigeration system of the inert gas type comprising a. a circuit for circulation of inert gas including an absorber and an evaporator subject to formation of frost, said absorber including a looped coil and a vessel into which absorption solution flows by gravity from said coil, b. a circuit for circulation of absorption solution including said absorber and a vapor-expulsion unit, said last-mentioned circuit having conduit means for conducting solution enriched in refrigerant from said absorber to said vapor-expulsion unit, said conduit means including a part which servEs as an analyzer and has a first liquid seal formed by a column of solution therein, c. a source of heat external to the system for heating said vapor-expulsion unit to expel vapor from solution therein, d. a condenser, e. means comprising a vapor line including said analyzer for conducting expelled vapor from the vapor space of said vapor-expulsion unit to said condenser and a condensate line for conducting condensate from said condenser to said evaporator for evaporation therein in the presence of inert gas to produce refrigeration, f. the expelled vapor being forced through the liquid column of said first liquid seal when expelled vapor is being conducted through said vapor line and said evaporator is producing refrigeration, g. means comprising a by-pass connection around said condenser for conducting expelled vapor at an elevated temperature from the vapor space of said vapor-expulsion unit to said evaporator to melt frost thereon, said by-pass connection having a downwardly extending portion communicating with the vapor space of said vapor-expulsion unit and an upwardly extending portion communicating with said evaporator, said downwardly and upwardly extending portions defining a trap in which a second liquid seal is formed by vaporous fluid condensed therein, h. the difference in height between the region at which the downwardly extending portion of said by-pass connection communicates with the vapor space of said vapor-expulsion unit and the bottom of the trap formed by said downwardly and upwardly extending portions in said by-pass connection being greater than the difference in height between the liquid surface level in said absorber vessel and the liquid level in said analyzer at the region thereof at which expelled vapor from said vapor space is introduced, i. the upper end of said upwardly extending portion of said by-pass connection being at a level higher than that of the upper end of said downwardly extending portion of said by-pass connection by a vertical height which is greater than the difference in height between the liquid surface level in said absorber vessel and the liquid level in said analyzer at the region thereof at which expelled vapor from said vapor space is introduced, and j. said vapor line having at least one part constructed and arranged to provide a third liquid seal formed by vaporous fluid condensed therein.
 8. An absorption refrigeration system as set forth in claim 7 in which said part of said vapor line providing said third liquid seal therein is disposed between said analyzer and said condenser.
 9. An absorption refrigeration system as set forth in claim 7 in which said part of said vapor line providing said third liquid seal is vertically disposed and includes a throttled zone above which vaporous fluid condensed and collects to form said third liquid seal responsive to the presence of vaporous fluid at a sufficient pressure in said vapor line below said throttled zone.
 10. An absorption refrigeration system as set forth in claim 9 in which said throttled zone is of circular form. 